Plague caused by the bacterium, Yersinia pestis (Y. pestis) remains an infectious disease of concern to public health due to the absence of a vaccine for humans and the isolation of antibiotic-resistant bacteria. Y. pestis is also a threat as a biological weapon. Although a subunit vaccine, comprised of the F1-V protein in alhydrogel, is known to provide antibody- based protection in small animal models, recent studies suggest the importance of inducing cellular immunity, in addition to humoral immunity, in the development of plague vaccines. In this proposal, we will achieve combined humoral and cellular immunity systemically, as well as at a mucosal surface, the lung, by targeting the Y. pestis LcrV protein directly to distinct DC subsets, i.e. DEC-205 or DCIR2 DCs in vivo. Our preliminary results show that 1) we can successfully generate LcrV conjugated mAbs specific for the DEC-205 and DCIR2 receptors expressed on two major DC subsets in mice, 2) DEC-205 or DCIR2 DC targeting induces enhanced cellular and humoral immunity, respectively, suggesting that distinct immune responses might be generated by different DC subsets, and 3) the increased antibody titers by DCIR2 DC targeting are closely correlated with the increased survival rate against challenge with pneumonic plague. Based on these findings, we propose three specific aims, where we will investigate 1) the quality and the quantity of both cellular and humoral immunity following DC subset targeting in several strains of mice, 2) its relationship to the protection efficacy, and 3) the underlying mechanisms that will be utilized in future vaccine design. PUBLIC HEALTH RELEVANCE: 1,000 to 3,000 cases of plague are still reported every year, and importantly Yersinia pestis is a NIAID category A priority pathogen in biodefense. Therefore, developing an effective plague vaccine, the goal of this proposal, is relevant to public health.